Ablation systems, probes, and methods for reducing radiation from an ablation probe into the environment

ABSTRACT

The ablation systems, ablation probes, and corresponding methods according to the present disclosure reduce or eliminate energy radiating from an ablation probe into the environment. Some ablation probes include a retractable sheath that shields at least the radiating portion of the ablation probe. The retractable sheath and/or the ablation probe may include conduits through which a fluid may flow to shield the radiating portion and to drive the retractable sheath to an extended state. Other ablation probes include apertures defined in the probe walls through which the fluid can flow to expand a balloon surrounding the radiating portion. Yet other ablation probes include a thermal indicator to indicate the temperature of the ablation probe to a user. The ablation systems include fluid circuits and associated mechanical controls for varying the contents and/or flow rate of the fluid provided to the radiating portion of the ablation probe.

BACKGROUND

1. Technical Field

The present disclosure generally relates to ablation systems. Moreparticularly, the present disclosure is directed to ablation systems,probes, and methods for reducing or eliminating energy radiating from anablation probe into a surgical environment.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures (which areslightly lower than temperatures normally injurious to healthy cells.)These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C., while maintaining adjacent healthy cells atlower temperatures where irreversible cell destruction will not occur.Other procedures using electromagnetic radiation to heat tissue includeablation and coagulation. These procedures are typically done todenature or kill the targeted tissue.

Many medical procedures and devices that use electromagnetic radiationare known in the art. Some of these procedures and devices are used totreat tissue and organs, such as the prostate, heart, liver, lung,kidney, and breast. These medical procedures and devices can be brokendown into two general categories: non-invasive and invasive.

Some non-invasive procedures involve treating tissue (e.g., a tumor)underlying the skin with microwave energy. The microwave energynon-invasively penetrates the skin to reach the underlying tissue.However, this non-invasive procedure may result in unwanted heating ofhealthy tissue. Thus, non-invasive procedures that use microwave energyrequire precise temperature control.

Some invasive procedures have been developed in which a microwaveantenna probe is either inserted directly into a point of treatment viaa normal body orifice or inserted percutaneously. These invasiveprocedures can provide better temperature control of the tissue beingtreated. Because of the small difference between the temperaturerequired for denaturing malignant cells and the temperature injurious tohealthy cells, a known heating pattern and predictable temperaturecontrol is important so that heating is confined to the tissue beingtreated. For instance, hyperthermia treatment at the thresholdtemperature of about 41.5° C. generally has little effect on mostmalignant growth of cells. However, at slightly elevated temperaturesabove the approximate range of 43° C. to 45° C., thermal damage to mosttypes of normal cells is routinely observed. Accordingly, great caremust be taken not to exceed these temperatures in healthy tissue.

To prevent damage to healthy tissue, the non-radiating portion of theablation probe is cooled with a cooling solution having dielectricproperties that are matched to the dielectric properties of the targettissue. When the ablation probe is removed from tissue, however, theprobe still has the ability to efficiently radiate microwave energybecause of the dielectric buffering provided by the cooling solution.Therefore, if the generator is still powering the probe after it isremoved from tissue, individuals near the probe may be unnecessarilyexposed to microwave energy.

SUMMARY

The ablation systems, ablation probes, and methods according to thepresent disclosure reduce or eliminate radiation from an ablation probeinto the environment and require few or no changes to a generator.

In one aspect, the present disclosure features an ablation probe. Theablation probe includes a shaft and a retractable sheath. The distalportion of the shaft includes a radiating portion that delivers energyto tissue. The retractable sheath surrounds at least the radiatingportion of the shaft. The retractable sheath prevents at least a portionof the energy from radiating outside of the retractable sheath andretracts as the shaft is inserted into tissue.

In some embodiments, the distal portion of the shaft includes a sharptip and the retractable sheath includes a tip cover coupled to a distalend of the retractable sheath. The tip cover encloses the sharp tip whenthe retractable sheath is in an extended state. In some embodiments, theablation probe includes a handle coupled to a proximal end of the shaftand the retractable sheath is coupled to a distal end of the handle.

In some embodiments, the retractable sheath is a compressible plasticcylinder and at least a portion of the compressible plastic cylinder iscoated with an electrically conductive material. In other embodiments,the retractable sheath is a compressible, electrically conductivematerial formed in the shape of a cylinder. The compressible,electrically conductive material may be a metal, such as copper. In someembodiments, the retractable sheath is electrically coupled to anelectrical ground.

In some embodiments, the retractable sheath includes at least one fluidconduit surrounding the shaft. For example, the retractable sheath mayinclude an inner wall, an outer wall, and at least one fluid conduitdisposed between these walls. The outer wall of the retractable sheathmay be coated with an electrically conductive material.

In another aspect, the present disclosure features an ablation system.The ablation system includes an ablation probe, a fluid source, a fluidpump, and a generator. The ablation probe includes a shaft having aproximal portion and a distal portion. The distal portion of the shaftincludes an antenna that delivers energy to tissue. The ablation probealso includes a sheath surrounding at least the radiating portion of theshaft. The sheath includes at least one fluid conduit defined within thesheath.

The fluid source of the ablation system is in fluid communication withthe at least one fluid conduit of the sheath. The fluid pump, in turn,is in fluid communication with the fluid source and the at least onefluid conduit. The fluid pump pumps a fluid through the at least onefluid conduit. The generator electrically couples to the antenna andsupplies electrical energy to the antenna.

In some embodiments, the fluid has dielectric properties that reduce theenergy radiating from the radiating portion of the shaft. For example,the fluid may include air, a mixture of cooling fluid and air, or amixture of cooling fluid and a dielectric material. In some embodiments,the energy delivered to tissue is microwave energy.

In some embodiments, the sheath is a retractable sheath that retractswhen the shaft is inserted in tissue. In some embodiments, the fluidpump supplies a fluid to the at least one fluid conduit under a workingpressure sufficient to extend the retractable sheath as the shaft isremoved from tissue.

In yet another aspect, the present disclosure features a method ofoperating an ablation probe to reduce radiation of energy from theablation probe to a surrounding surgical environment. The methodincludes retracting a sheath surrounding at least a radiating portion ofan ablation probe. The sheath retracts along a longitudinal axis of theablation probe toward a proximal end of the ablation probe as theradiating portion of the ablation probe is advanced towards a targetvolume of tissue. The method also includes advancing the sheath alongthe longitudinal axis of the ablation probe toward a distal end of theprobe as the radiating portion of the ablation probe is removed fromtissue such that the sheath surrounds at least the radiating portion ofthe ablation probe.

In some embodiments, the method further includes pumping a fluid into atleast one fluid conduit disposed in the sheath. The fluid may haveproperties that at least reduce the energy radiating from the radiatingportion of the ablation probe to the environment. The fluid may benitrogen or air.

In the present disclosure, the term “proximal” refers to the portion ofa structure that is closer to a user, while the term “distal” refers tothe portion of the structure that is farther from the user.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described herein withreference to the drawings wherein:

FIG. 1 is a diagram of a microwave ablation system according toembodiments of the present disclosure;

FIG. 2A is an perspective view of a distal portion of an ablation probeaccording to some embodiments of the present disclosure;

FIG. 2B is a longitudinal, cross-sectional view of a feed line portionof the ablation probe of FIG. 2A;

FIG. 2C is a transverse, cross-sectional view of the feed line portionof the ablation probe of FIG. 2A taken along the line 2C-2C of FIG. 2B.

FIG. 2D is an internal perspective view of the distal portion of theablation probe of FIG. 2A illustrating the coaxial inflow and outflowchannels.

FIG. 3 is a schematic, cross-sectional side view of an ablation probehaving a retractable sheath according to some embodiments of the presentdisclosure;

FIG. 4 is a schematic, cross-sectional side view of the ablation probeof FIG. 3 in which the retractable sheath is in a retracted state;

FIG. 5A is a schematic, perspective view of a retractable sheathaccording to other embodiments of the present disclosure;

FIG. 5B is a schematic, perspective view of the retractable sheath ofFIG. 5A in a retracted state;

FIG. 6 is a schematic, cross-sectional side view of an ablation probeincorporating an expandable balloon according to some embodiments of thepresent disclosure;

FIG. 7A is a schematic, perspective view of an ablation probe having apassive thermal sensor according to some embodiments of the presentdisclosure;

FIG. 7B is a schematic, cross-sectional side view of the passive thermalsensor disposed on the ablation probe of FIG. 7A;

FIG. 8A is a diagram of an ablation probe incorporating a fluid circuitfor feeding shielding fluid to the ablation probe;

FIGS. 8B and 8C are schematic diagrams of a fluid circuit for adjustingthe properties of the shielding fluid fed to the ablation probeaccording to some embodiments of the present disclosure; and

FIGS. 9A and 9B are schematic diagrams of a fluid circuit for adjustingthe properties of the fluid fed to the ablation probe according to otherembodiments of the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are described belowwith reference to the accompanying drawings.

Generally, the present disclosure relates to systems and correspondingmethods for reducing or eliminating energy that radiates from ablationprobes into the environment. These systems and corresponding methodsrequire few or no changes to the electrosurgical generator that suppliespower to the ablation probe. The systems include various shieldingmechanisms for shielding individuals from unnecessary energy radiatingfrom the ablation probe when it is removed from tissue.

The ablation systems according to the present disclosure include aretractable sheath or shield that shields at least the radiating portionof the ablation probe to reduce or eliminate the radiation of energy(e.g., microwave energy) into the environment. The retractable sheathmay include conduits through which a shielding fluid flows to shield theradiating portion of the ablation probe. The shielding fluid may also beused to drive the retractable sheath from a retracted state to anextended state. In some embodiments, the ablation probe includesapertures formed in the walls of the ablation probe near the radiatingportion and a balloon surrounding the ablation probe to cover theapertures. In these embodiments, the shielding fluid flows through theapertures into the balloon to expand the balloon surrounding theradiating portion.

The ablation systems also include fluid circuits having mechanicalcontrols that vary the contents and/or flow rate of the shielding fluidthat cools the radiating portion. For example, when the user operates(e.g., applies force to) the mechanical controls (e.g., the user useshis/her finger to depress a button), the cooling solution flows to theradiating portion. When the user again operates (e.g., removes forcefrom) the mechanical controls (e.g., the user removes his/her fingerfrom the button or depresses the button again), the shielding fluid or amixture of the cooling solution and the shielding fluid is supplied tothe radiating portion. The cooling solution may include cooled water ora water-based solution. The shielding fluid may also include a mixtureof water and small particles of dielectric material.

An ablation system according to embodiments of the present disclosureincludes an ablation probe 12 having an antenna and/or an electrode thatdelivers energy to tissue. FIG. 1 illustrates an ablation system 10including the ablation probe 12, a microwave generator 14, and a coolingfluid supply 33. The ablation probe 12 is coupled to the microwavegenerator 14 via a flexible coaxial cable 16. The ablation probe 12 isalso fluidly coupled to the cooling fluid supply 33 via a fluid supplyline or conduit 86 and a fluid return line or conduit 88. Cooling fluidleaves the ablation probe 12 through the fluid return line 88.

In a closed-loop cooling fluid system, the ablation probe 12 is fluidlycoupled to the cooling fluid supply 33 via fluid return line 88 andcooling fluid is cycled through the cooling fluid supply 33. In anopen-loop cooling fluid system, the cooling fluid flows through thefluid return line 88 to a drain or other suitable disposable receptacleand new cooling fluid is supplied to the cooling fluid supply 33 from acooling fluid reservoir 36 or other suitable source of cooling fluid.

The ablation probe 12 generally includes a connection hub 22 and a shaft15. The distal portion of the shaft 15 includes a radiating portion 18and the proximal portion of the shaft 15 includes a feed line 20. Theconnection hub 22 connects the microwave generator 14 and the coolingfluid supply 33 to the ablation probe 12. The microwave signal isproduced by the microwave generator 14, transmitted through the flexiblecoaxial cable 16, which connects to the connection hub 22, and theconnection hub 22 facilitates the transfer of the microwave signal tothe feed line 20. The connection hub 22 further facilitates the transferof cooling fluid to and from the feed line 20. Cooling fluid, providedfrom the fluid pump 34 of the cooling fluid supply 33, is provided tothe connection hub 22 through the fluid supply line 86. The connectionhub 22 transfers the cooling fluid from the fluid supply line 86 to thecooling fluid supply lumen (not explicitly shown) of the feed line 20.

The cooling fluid, after being circulated through the feed line 20 andradiating portion 18 of the ablation probe 12, is returned to theconnection hub 22 through the return lumen (not explicitly shown) of thefeed line 20. Connection hub 22 facilitates the transfer of the coolingfluid from the return lumen (not explicitly shown) to the fluid returnline 88.

In one embodiment, the microwave ablation system 10 includes aclosed-loop cooling system wherein the fluid return line 88 returns thecooling fluid to the fluid pump 34 of the cooling fluid supply 33. Thecooling fluid supply 33 cools the returned cooling fluid from the fluidreturn line 88 before recirculating at least a portion of the returnedcooling fluid through the microwave ablation system 10.

In another embodiment, the fluid return line 88 connects to a suitabledrain and/or reservoir (e.g., cooling fluid from the ablation probe 12is not returned to the cooling fluid supply 33). Cooling fluid reservoir36 of the cooling fluid supply 33 provides a continuous supply ofcooling fluid to the fluid pump 34. Cooling fluid reservoir 36 may alsoinclude a temperature control system (not shown) configured to maintainthe cooling fluid at a predetermined temperature. Coolant fluid mayinclude any suitable liquid or gas, including air, or any combination ofliquid and gas.

The ablation probe 12 may include any suitable microwave antenna 40 suchas, for example, a dipole antenna, a monopole antenna and/or a helicalantenna. The microwave generator 14 may be configured to provide anysuitable electrical energy within an operational frequency from about300 MHz to about 10 GHz. The physical length of the microwave antenna 40is dependent on the frequency of the microwave energy signal generatedby the microwave generator 14. For example, in one embodiment, amicrowave generator 14 providing a microwave energy signal at about 915MHz drives an ablation probe 12 that includes a microwave antenna 40with a physical length of about 1.6 cm to about 4.0 cm.

FIG. 2A is an enlarged view of the distal portion of the ablation probe12 of FIG. 1 and includes a feed line 20, a proximal radiating portion42 and a distal radiating portion 44. The proximal radiating portion 42and the distal radiating portion 44 form a dipole antenna 40. Asillustrated in FIG. 2A, the proximal radiating portion 42 and the distalradiating portion 44 are unequal thereby forming an unbalanced dipoleantenna 40. The ablation probe 12 includes a sharp tip 48 having atapered end 24 that terminates, in one embodiment, at a pointed tip 26to allow for insertion into tissue with minimal resistance at a distalend of the radiating portion 18. In another embodiment, the radiatingportion 18 is inserted into a pre-existing opening or catheter and thetip may be rounded or flat.

The sharp tip 48 may be machined from various stock rods to obtain adesired shape. The sharp tip 48 may be attached to the distal radiatingportion 44 using various adhesives or bonding agents, such as an epoxysealant. If the sharp tip 48 is metal, the sharp tip 48 may be solderedto the distal radiating portion 44 and may radiate electrosurgicalenergy. In another embodiment, the sharp tip 48 and a distal radiatingportion 44 may be machined as one piece. The sharp tip 48 may be formedfrom a variety of heat-resistant materials suitable for penetratingtissue, such as ceramic, metals (e.g., stainless steel) and variousthermoplastic materials, such as polyetherimide or polyimidethermoplastic resins, an example of which is Ultem® sold by GeneralElectric Co. of Fairfield, Conn.

FIG. 2B is a longitudinal cross-sectional view of a section of the feedline 20 of the ablation probe 12 of FIG. 1, and FIG. 2C is a transverse,cross-sectional view of the feed line 20 of the ablation probe 12 ofFIG. 2B. Feed line 20 is coaxially formed with an inner conductor 50 atthe radial center surrounded by a dielectric layer 52 and an outerconductor 56.

The inflow hypotube 55 is spaced apart and disposed radially outwardfrom the outer conductor 56. The outer surface of the outer conductor 56b and the inner surface of the inflow hypotube 55 a form an inflowchannel 17 i allowing cooling fluid to flow distally through the feedline 20 of the ablation probe 12 as indicated by the arrows within theinflow channel 17 i. The inflow hypotube 55 may be formed from a varietyof heat-resistant materials, such as ceramic, metals (e.g., stainlesssteel), various thermoplastic materials, such as polyetherimide orpolyimide thermoplastic resins (e.g., Ultem®), or composite medicaltubing, an example of which is PolyMed® sold by Polygon of Walkerton,Ind. In one embodiment, the inflow hypotube 55 may have a wall thicknessless than about 0.010 inches. In another embodiment, the inflow hypotube55 may have a wall thickness less than about 0.001 inches.

The outer hypotube 57 is spaced apart from, and radially outward from,the inflow hypotube 55. The outer surface of the inflow hypotube 55 band the inner surface of the outer hypotube 57 a form an outflow channel17 o that allows cooling fluid to flow proximately through the feed line20 of the ablation probe 12 as indicated by the arrows within theoutflow channel 17 o. The outer hypotube 57 may be formed from a varietyof heat-resistant materials, such as ceramic, metals (e.g., stainlesssteel), various thermoplastic materials, such as polyetherimide,polyimide thermoplastic resins (e.g., Ultem®), or composite medicaltubing (e.g., PolyMed®). In one embodiment, the outer hypotube 57 mayhave a wall thickness less than about 0.010 inches. In anotherembodiment, the outer hypotube 57 may have a wall thickness less thanabout 0.001 inches.

The substantially radially concentric cross-sectional profile of thefeed line, as illustrated in FIG. 2C, provides uniform flow of fluid inboth the inflow channel 17 i and the outflow channel 17 o. For example,an inflow channel gap G1 defined between the outer surface of the outerconductor 56 b and the inner surface of the inflow hypotube 55 a issubstantially uniform around the circumference of the outer conductor56. Similarly, an outflow channel gap G2 defined between the outersurface of the inflow hypotube 55 b and the inner surface of the outerhypotube 57 is substantially uniform around the circumference of theinflow hypotube 55.

In addition, the cross-sectional area of the inflow channel 17 i and theoutflow channel 170 (i.e., the effective area of each channel in whichfluid flows) is the difference between the area at the outer surface ofthe inflow channel 17 i and the outflow channel 17 o (i.e., the area atthe inner diameter of the inflow hypotube 55 and the area at the innerdiameter of the outer hypotube 57, respectively) and the area at theinner surface of the inflow channel 17 i and the outflow channel 17 o(i.e., the area at the outer diameter of the outer conductor 56 and thearea at the outer diameter of the inflow hypotube 55). Thecross-sectional area of the inflow channel 17 i and the outflow channel17 o is substantially uniform along the longitudinal length of the feedline 20. In addition, transverse shifting of the inflow hypotube 55within the outer hypotube 57 or transverse shifting of the outerconductor 56 within the inflow hypotube 55, may create a non-uniforminflow or outflow channel gap G1, G2, but will not affect thecross-sectional area of either the inflow channel 17 i and/or theoutflow channel 17 o.

FIG. 2D, which is a perspective view of the radiating portion 18 of FIG.1, illustrates the inflow fluid flow pathways. The radiating portion 18is formed by inserting the distal portion of the feed line 20 into themicrowave antenna 40.

The feed line 20 is configured to provide cooling fluid and a microwaveenergy signal to the microwave antenna 40. As discussed hereinabove, thefeed line 20 provides cooling fluid through the inflow channel 17 iformed between the inflow hypotube 55 and the outer conductor 56 of thefeed line 20. The feed line 20 also provides a microwave energy signalbetween the inner conductor 50 and the outer conductor 56.

The antenna 40 includes a tapered inflow transition collar 53, achanneled puck 46, a distal radiating portion 44, including a pluralityof antenna sleeve stops 68 a-68 d, and a sharp tip 48. The feed line 20,when inserted into the antenna 40, connects the outer conductor 56 tothe tapered inflow transition collar 53 and the inner conductor 50 tothe distal radiating portion 44.

When the radiating portion 18 is removed from tissue after energy, e.g.,microwave energy, is applied to a tissue volume, a shield is placedbetween the radiating portion 18 and the patient and clinician. As shownin FIG. 3, the shield may include a retractable sheath 302 thatsurrounds the entire length of the shaft 15 in a fully-extended state.The retractable sheath includes a retractable sheath 302 and a tip cover304. In some embodiments, the retractable sheath 302 is a compressibleplastic cylinder. The tip cover 304 covers the pointed tip 26 to preventinjury. The tip cover 304 may be made of a semi-rigid or rigid material(e.g., a semi-rigid or rigid plastic). The retractable sheath 302attaches to the handle 320.

In some embodiments, the retractable sheath 302 and/or the tip cover 304are made of a compressible, electrically conductive material formed inthe shape of a cylinder. The compressible, electrically conductivematerial may be a metal, such as copper. In other embodiments, theretractable sheath 302 and/or the tip cover 304 are coated on theirinner and/or outer surfaces with a compressible, electrically conductivematerial. The retractable sheath 302 and/or the tip cover 304 may beelectrically coupled to electrical ground 315 to form an electromagneticenclosure, which contains the electromagnetic fields generated by theradiating portion 18 to prevent radiation into the environment.

Because the retractable sheath 302 is compressible, the tip cover 304 ismovable along a longitudinal axis 314 of the shaft 15. As shown in FIG.4, when the shaft 15 is inserted in tissue 402, the bottom surface 310of the tip cover 304 mates with the outside surface 404 of a targetvolume of the tissue 402, which pushes the tip cover 304 towards thehandle 320 and compresses the retractable sheath 302. When the shaft 15is removed from tissue 402, the tip cover 304 and the retractable sheath302 decompress and extend to cover the entire length of the shaft 15.

FIG. 5A shows a retractable sheath 500 having fluid conduits 514, 516. Acooling fluid 524, 526 having appropriate dielectric properties flowsthrough the fluid conduits 514, 516 to form a fluid shield around theradiating portion 18 of the shaft 15. The fluid conduits 514, 516 areformed between the inner surface of the outer wall 510 and the outersurface of the inner wall 512. Multiple conduits may be formed in theretractable sheath 500 by forming conduit walls 513, 515 that extendbetween the inner surface of the outer wall 510 and the outer surface ofthe inner wall 512. The conduit wall 513 forms a first fluid conduit 514and the conduit wall 515 forms a second fluid conduit 516. In otherembodiments, more than two conduit walls may be formed in theretractable sheath 500 to provide more than two fluid conduits.

The conduit walls 513, 515 shown in FIGS. 5A and 5B have a linear shapealong the length of the retractable sheath 500. In other embodiments,however, the conduit walls 513, 515 may have a non-linear shape, such asa curved shape.

As shown in FIG. 5A, the fluid conduit 514 may carry a cooling fluid 524to the distal end 521 of the retractable sheath 500 and the fluidconduit 516 may carry the cooling fluid 524 to the proximal end of theretractable sheath 500. The retractable sheath 500 may include a tipcover (not shown) at the distal end 521 of the retractable sheath 500that directs the cooling fluid 524 flowing in the fluid conduit 514 tothe fluid conduit 516. In this manner, the cooling fluid 524 may becirculated through the retractable sheath 500.

As illustrated in FIG. 5B, when the shaft 15 is placed within tissue,the retractable sheath 500 compresses to a retracted state. When theshaft 15 is removed from the tissue, the fluid pump 34 supplies acooling fluid 524 to the retractable sheath 500 under a working pressuresufficient to extend the retractable sheath 500 to the extended stateshown in FIG. 5A.

In some embodiments, the metal-coated retractable sheath of FIGS. 3 and4 is combined with the retractable sheath 500 of FIGS. 5A and 5B. Forexample, the retractable sheath 500 may be coated with a metal or anyother electrically conductive material.

FIG. 6 shows a cross-sectional side view of an ablation probe 600, e.g.,a microwave ablation probe, having an expandable balloon 610. The shaft615 is a hollow elongated shaft or introducer having a wall 616 thatencloses an electrical conductor having an antenna 618, e.g., amicrowave antenna, and a coaxial cable 620. The coaxial cable 620 iselectrically coupled to the antenna 618 and supplies energy, e.g.,microwave energy, to the antenna 618. The space between the innersurface of the wall 616 and the outer surfaces of the antenna 618 andthe coaxial cable 620 forms a fluid conduit 622 through which coolingfluid flows to cool the antenna 618.

The ablation probe 600 also includes multiple apertures 604 formed inthe wall 616 of the shaft 615. The apertures 604 are formed around theshaft 15 along the length of the antenna 618. Alternatively, theapertures 604 are formed around the shaft 15 along a portion of thelength of the antenna 618 or near the antenna 618. The expandableballoon 610 is disposed on the outer surface of the wall 616 and isconfigured to cover the apertures 604.

When the ablation probe 600 is placed in tissue and is transferringenergy to the tissue, the balloon 610 maintains a normal state 626 incontact with or in close proximity to the outer surface of the wall 616.When the ablation probe 600 is removed from the tissue, the fluidconduit 622 carries a shielding fluid 624, which may be a pressurizedfluid, to the apertures 604. The shielding fluid 624 flows through theapertures 604 and expands the balloon 610 to an expanded state 628. Inthe expanded state 628, the balloon 610 defines and holds a volume 630of shielding fluid 624 around the antenna 618. The volume 630 ofshielding fluid 624 absorbs and attenuates the energy radiating from theantenna 618 before the energy can radiate into the environment.

In some embodiments, the ablation probe 600 interfaces with the fluidpump 34 of FIG. 1 that is configured to supply a cooling fluid to theablation probe 600 at a pressure level sufficient to maintain theballoon 610 in an expanded state 628 when the ablation probe 600 isoutside of tissue. But, when the ablation probe 600 is inserted intotissue, the tissue compresses the balloon 610 against the outer surfaceof the shaft 615 to bring the balloon 610 back to its normal state 626.When the ablation probe 600 is removed from tissue, the pressure of thecooling fluid expands the balloon 610 to an expanded state 628 and formsa large volume of fluid around the antenna 618 to absorb most of theelectromagnetic energy radiating from the antenna 618.

FIG. 7A is a perspective view of an ablation probe 700 having atemperature indicator 702 (e.g., a passive temperature indicator)disposed on the outer surface of the handle 306. The temperatureindicator 702 may optionally be disposed on the outer surface of theshaft 15. The temperature indicator 702 is a device that displays thetemperature of the handle 306 or the shaft 15. For example, thetemperature indicator 702 may include a material that varies in color orbrightness as the temperature of the handle 306 or the shaft 15 varies.In particular, the brightness of the material may increase as thetemperature of the handle 306 or the shaft 15 increases.

FIG. 7B illustrates an embodiment of the temperature indicator 702. Thetemperature indicator 702 includes a layer of thermal gel 710, e.g., agel pad, disposed on the surface of the handle 308 and thermal paper 712disposed on the layer of thermal gel 710. The layer of thermal gel 710may attach to the handle 308 (or the shaft 15) through a thermallyconductive adhesive.

As described above, the thermal paper 712 may change color to indicate achange in temperature of the handle 308 or shaft 15 to which thetemperature indicator 702 is attached. Thus, when the ablation probe 700is removed from tissue, any energy radiating from the antenna 618 heatsthe shaft 15 and the handle 308 through thermal conduction. The heat inthe handle 308 then transfers through the layer of thermal gel 710 tothe thermal paper 712 and changes the color of the thermal paper 712.The changed color of the thermal paper 712 indicates to the clinicianthat the temperature of the handle 308 exceeds a predetermined level.

In some embodiments, the temperature indicator 702 is disposed on thehandle 306 of an ablation probe that also includes the retractablesheath 302 of FIGS. 3 and 4. In other embodiments, the temperatureindicator 702 is disposed on the retractable sheath 302 of FIGS. 3 and 4in case the retractable sheath 302 absorbs heat from the radiatingportion 18 of the shaft 15 and heats up.

In some embodiments, the ablation probe 12 is reconfigured to feed ashielding fluid to the radiating portion 18 of the shaft 15 in order toreduce or eliminate radiation from the shaft 15 into the environment. Asillustrated in FIG. 8A, the ablation probe 12 includes a fluid circuitmodule 800 that is fluidly coupled to a shielding fluid source 801 via asecond fluid supply conduit 811. As described in greater detail below,the fluid circuit module 800 receives shielding fluid from the shieldingfluid source 801 and supplies it to the radiating portion of the shaft15 when the shaft 15 is removed from tissue after an ablation procedureis completed.

The fluid circuit module 800 includes a button 804 that allows a user ofthe ablation probe 12 to control the supply of shielding fluid to theradiating portion 18 of the shaft 15. For example, the fluid circuitmodule 800 may be configured (1) to supply the cooling fluid to theradiating portion 18 of the shaft 15 when the user depresses the button804 and (2) to supply a mixture of the cooling fluid and the shieldingfluid to the radiating portion 18 of the shaft 15 when the user releasesthe button 804. Alternatively, the fluid circuit module 800 may beconfigured (1) to supply the cooling fluid to the radiating portion 18of the shaft 15 when the user depresses the button 804 a first time and(2) to supply a mixture of the cooling fluid and the shielding fluid tothe radiating portion 18 of the shaft 15 when the user depresses thebutton 804 a second time.

FIGS. 8B and 8C are schematic diagrams of an embodiment of the fluidcircuit module 800 of FIG. 8A. FIGS. 8B and 8C illustrate the operationof an embodiment of the fluid circuit module 800 that allows a user toselect whether to supply a cooling fluid or a mixture of the coolingfluid and a shielding fluid to the radiating portion 18 of the shaft 15of the ablation probe 12. As shown in FIG. 8A, the fluid circuit 800includes the fluid supply conduit 86 (hereinafter referred to as thefirst fluid supply conduit 86) fluidly coupled between the fluid pump 34of FIG. 1 and a common fluid supply conduit 810. The common fluid supplyconduit 810, in turn, is in fluid communication with the shaft 15.

The fluid circuit 800 also includes a bypass fluid conduit 822 that isfluidly coupled to the first fluid supply conduit 86 through a bypassfluid chamber 805. The flow of fluid through the bypass fluid conduit822 is controlled by a bypass valve assembly 808. The bypass valveassembly 808 includes a piston 806 that is movable in a verticaldirection within the bypass fluid chamber 805. The bypass valve assembly808 also includes a button 804 or other similar manual control mechanismcoupled to the piston 806 that allows a user to move the piston 806within the bypass fluid chamber 805.

In operation, when a user depresses the button 804 to move the piston806 to the bottom of the bypass fluid chamber 805, a first fluid 840supplied by the fluid pump 34 flows through the first fluid supplyconduit 86, the bypass fluid chamber 805, and the common fluid supplyconduit 810 to the shaft 15. The first fluid 840, however, does notenter the bypass fluid conduit 822 because the piston 806 covers theinlet of the bypass fluid conduit 822. The common fluid supply conduit810 supplies the first fluid 840 to the shaft to facilitate theradiation of microwave energy from the radiating portion of theconductor disposed within the shaft 15. The fluid circuit 800 alsoincludes a fluid return line 88 that carries the first fluid 840returned from the shaft 15 to the fluid pump 34.

As shown in FIG. 8B, the fluid circuit 800 also includes the secondfluid supply conduit 811, which supplies a second fluid 842 (e.g., ashielding fluid or a cooling fluid) to the common fluid conduit 810. Thecommon fluid conduit 810 delivers the second fluid 842 to the shaft tominimize or prevent radiation of electromagnetic energy from theradiating portion of the shaft 15 to tissue or the surroundingenvironment. The second fluid 842 may be any fluid that absorbs theelectromagnetic energy radiating from the antenna. For example, thesecond fluid 842 may be a liquid solution containing particles thatabsorb electromagnetic energy radiating from the antenna.

To pump the second fluid 842 through the second fluid supply conduit811, the fluid circuit 800 incorporates a second fluid pump assembly825. The second fluid pump assembly 825 includes a fluid pump 830 and animpeller 828 coupled to the fluid pump 830. As shown in FIG. 8B, thefluid pump 830 is positioned within the second fluid supply conduit 811.The impeller 828 is operatively coupled to the fluid pump 830 through ashaft 829. The impeller 828 is positioned within the bypass fluidconduit 822 so that the first fluid 840 flowing through the bypass fluidconduit 822 causes the impeller to rotate and drive the fluid pump 830.In other embodiments, the second fluid pump assembly 825 may includedifferent components that use the flow of the first fluid 840 flowingthrough the bypass fluid conduit 822 to cause the second fluid 842 toflow in the second fluid supply conduit 811.

The second fluid supply conduit 811 also includes a check valve 832 thatallows the second fluid to flow in one direction from a second fluidsource (not shown) to the common fluid conduit 810. The check valve alsoprevents any first fluid 840 flowing in the first fluid supply conduit86 from entering the second fluid supply conduit 811. In someembodiments, the check valve 832 is a duck bill valve.

When the user desires to apply microwave energy to tissue, the userdepresses the button 804 with his/her finger to cause the first fluid840 to flow through the common fluid supply conduit 810 to the radiatingportion of the shaft 15. As described above, the first fluid 840increases the efficiency of the radiating portion of the microwaveconductor disposed within the shaft 15. When the user desires to stopapplying microwave energy to tissue, the user removes his/her fingerfrom the button 804 or depresses the button 804 a second time to causethe second fluid 842 to flow through the common fluid supply conduit 810to the shaft 15 to shield the radiating portion of the microwaveconductor. For example, the bypass valve assembly 808 may be springloaded so that the bypass valve assembly 808 returns to the up position809 when the user removes pressure from the button 804.

In the up position 809, the piston 806 prevents the first fluid 840 fromflowing to the common fluid supply conduit 810 and directs the firstfluid 840 into the bypass fluid conduit 822. The first fluid 840 flowsthrough the impeller 828 causing it to rotate and drive the fluid pump830 through the shaft 829 of the fluid pump assembly 825. Then, thefluid pump 830 pumps the second fluid 842 from a second fluid source(not shown) through the check valve 832 to the common fluid supplyconduit 810. The first fluid 840 flows out of the bypass fluid conduit822 and into the fluid return conduit 820, which carries the first fluid840 to the fluid pump 34. The second fluid 842 flows to the shaft 15 viathe common fluid supply conduit 810 and then returns from the shaft 15via the fluid return conduit 820. The second fluid 842 mixes with thefirst fluid 840 and returns to the fluid pump 34.

FIGS. 9A and 9B show another embodiment of a fluid circuit 900 thatallows the user to select whether to supply a cooling fluid or a mixtureof a cooling fluid and another fluid to the shaft 15. Similar to theembodiment of FIGS. 8B and 8C, the fluid circuit 900 includes a firstfluid supply conduit 86 and a second fluid supply conduit 904 that feedinto a common fluid supply conduit 920. Unlike the embodiment of FIGS.8B and 8C, however, the first fluid supply conduit 86 includes a firstrecessed portion 910 and the second fluid supply conduit 811 includes asecond recessed portion 914. The first recessed portion 910 is shapedand dimensioned to receive an impeller 908 and the second recessedportion 914 is shaped and dimensioned to receive a fluid pump 912. As inthe embodiment FIGS. 8B and 8C, the impeller 908 and fluid pump 912 areoperatively coupled to each other and form a portion of a fluid valveassembly 915.

The fluid valve assembly 915 also includes a button 906 or other controlmechanism that is coupled to the impeller 908. The first fluid supplyconduit 86 includes a first recessed portion 910 and the second fluidsupply conduit 904 includes a second recessed portion 914. The fluidvalve assembly 915 can move between an up position and a down position913 within the first and second recessed portions 910, 914. The fluidvalve assembly 915 is spring loaded with a spring 916 that is positionedbetween the bottom surface of the second recessed portion 914 and thebottom surface of the second fluid pump 912 to maintain the fluid valveassembly 915 in the up position 911. Other types and arrangements ofsprings could also be used to maintain the fluid valve assembly 915 inthe up position 911.

As shown in FIG. 9A, if the button 906 is depressed, a first fluid 940flows through the first fluid supply conduit 86 to the common fluidsupply conduit 920, while no fluid flows through the second fluid supplyconduit 904. This is because the impeller 908 is positioned in the firstrecessed portion 910 away from the flow of the first fluid 940 so thatthe first fluid 940 cannot cause the impeller 908 to rotate and drivethe second fluid pump 912. Also, the second fluid pump 912 is positionedin the second recessed portion 914 so that the second fluid pump 912cannot draw the second fluid 942 through the second fluid supply conduit904.

As shown in FIG. 9B, when the button 905 is released, the impeller 908moves into the flow of the first fluid 940 and the second fluid pump 912moves into the flow path of the second fluid 942. The flow of the firstfluid 940 causes the impeller 908 to rotate. The impeller 908, in turn,drives the second fluid pump 912. In operation, the second fluid pump912 draws the second fluid 942 through the second fluid supply conduit904 and into a mixing area 924 where the first fluid 940 flowing throughthe impeller 908 mixes with the second fluid 942 to form a third fluid922. The fluid valve assembly 915 may include gears that control thespeed of the second fluid pump 912 and thus the flow rate of the secondfluid 942 to control the ratio of first fluid 940 to second fluid 942 inthe third fluid 922. In this manner, the properties of the third fluid922 may be adjusted to improve its ability to shield the radiatingportion of the ablation probe from nearby tissue or the externalenvironment.

In some embodiments, the first fluid 940 is a water-based buffersolution and the second fluid 942 is air or a similar gas, such asnitrogen, which agitates the water-based buffer solution when the button905 is released. The air and buffer solution mixture may have differentdielectric properties than the buffer solution alone. These differentdielectric properties would hinder unnecessary energy transfer from theradiating portion of the shaft or probe into the environment.

The structures and methods described above for reducing or eliminatingenergy that radiates from ablation probes into the environment may beused in any combination to achieve varying levels of shielding. Forexample, an ablation system may incorporate the apertures 604 and theballoon 610 of FIG. 6, and the fluid circuit module 800 of FIGS. 8A-8C.In such an ablation system, the fluid circuit module 800 suppliesshielding fluid to the balloon 610 through the apertures 604 when a userremoves his/her finger from the button 804 at the completion of anablation procedure. The shielding fluid is supplied to the balloon 610at a pressure level sufficient to expand the balloon 610 when theablation probe is removed from the tissue.

In another example, an ablation system may incorporate the retractablesheath 500 of FIGS. 5A-5B (i.e., the retractable sheath having fluidconduits) and the fluid circuit 900 of FIGS. 9A-9B. In such an ablationsystem, a mixture of shielding fluid and cooling fluid is supplied tothe retractable sheath 500 when a user removes his/her finger from thebutton 804 at the completion of an ablation procedure. In yet anotherexample, an ablation system may incorporate the temperature indicator702 of FIGS. 7A and 7B and the fluid circuit 800 of FIGS. 8A-8C.

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. An ablation probe comprising: a shaft having aproximal portion and a distal portion, the distal portion comprising aradiating portion configured to deliver energy to tissue; and aretractable sheath surrounding at least the radiating portion of theshaft, the retractable sheath configured to prevent at least a portionof the energy from radiating outside of the retractable sheath, theretractable sheath configured to retract as the shaft is inserted intotissue, wherein a distal portion of the retractable sheath includes arigid tip cover and a proximal portion of the retractable sheathincludes a compressible, electrically conductive material formed in theshape of a cylinder and includes at least two fluid conduits configuredto surround the shaft, and wherein the at least two fluid conduitsinclude a first fluid conduit that provides cooling fluid to a distalend of the retractable sheath and a second fluid conduit that returnscooling fluid to a proximal end of the retractable sheath.
 2. Theablation probe according to claim 1, wherein the distal portion of theshaft includes a sharp tip, and wherein the rigid tip cover isconfigured to enclose the sharp tip when the retractable sheath is in anextended state.
 3. The ablation probe according to claim 1, furthercomprising a handle coupled to a proximal end of the shaft, theretractable sheath coupled to a distal end of the handle.
 4. Theablation probe according to claim 1, wherein the proximal portion of theretractable sheath includes a compressible plastic cylinder and at leasta portion of the compressible plastic cylinder is coated with anelectrically conductive material.
 5. The ablation probe according toclaim 1, wherein the retractable sheath is electrically coupled to anelectrical ground.
 6. The ablation probe according to claim 1, whereinthe compressible, electrically conductive material is a metal.
 7. Theablation probe according to claim 6, wherein the metal is copper.
 8. Theablation probe according to claim 1, wherein the retractable sheathincludes an outer wall coated with an electrically conductive material.9. The ablation probe according to claim 1, wherein the ablation probefurther comprises a temperature indicator disposed on the shaft.
 10. Theablation probe according to claim 9, wherein the temperature indicatorincludes a layer of thermal gel and thermal paper disposed on the layerof thermal gel.
 11. The ablation probe according to claim 10, whereinthe thermal paper changes color when the shaft changes temperature.